core/validatorapi: fix dynamic path proxy metric

[KaloyanTanev]

Prometheus metrics were growing their cardinality uncontrollably on proxied requests that had slot/epoch/pubkey/val_idx in them.

category: bug
ticket: none

[Copilot]

Pull request overview

This PR fixes unbounded Prometheus label cardinality for proxied validator API requests by normalizing dynamic URL path segments into placeholder tokens before recording the core_validatorapi_proxy_request_latency_seconds histogram.

Changes:

• Replaced raw proxied request path metric labels with a bounded label produced by proxyPathLabel.
• Added path-segment normalization to collapse hex (0x…), numeric (123…), and /peers/{id} segments into placeholders.
• Added unit tests covering expected label normalization and a bounded-cardinality assertion for distinct block roots.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated no comments.

File	Description
core/validatorapi/metrics.go	Introduces proxyPathLabel and uses it for proxy latency metric labels to prevent high-cardinality metrics.
core/validatorapi/metrics_internal_test.go	Adds tests validating path normalization behavior and ensuring distinct dynamic roots collapse to the same label.

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[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 57.03%. Comparing base (9a39a98) to head (d9cd27b).
⚠️ Report is 2 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #4553      +/-   ##
==========================================
+ Coverage   56.98%   57.03%   +0.04%     
==========================================
  Files         245      245              
  Lines       33150    33168      +18     
==========================================
+ Hits        18892    18918      +26     
+ Misses      11870    11861       -9     
- Partials     2388     2389       +1     

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[sonarqubecloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube Cloud